int l = str.length();
      if(l==0){
         String k = "";
         return k;
      }
      
      else if(l % 2 == 1){
         char date[]={str.charAt(l/2)};
         String k = new String(date);
         return k;
      }
      else{
         char data[]={str.charAt(l/2-1),str.charAt(l/2)};
         String kk = new String(data);
         return kk;
      }